1. Field of the Invention
The present invention is generally related to a gas barrier composite film and its preparation method, and more particularly to a transparent gas barrier composite film and its preparation method using polyvinyl alcohol and graphene oxide.
2. Description of the Prior Art
A transparent film with high gas barrier can be not only used as packaging materials and but also gradually extensively applied as substrates or sealing films of electronic devices accompanying with development of flexible electronic products. Film deposition or atomic layer deposition to deposit atomic or molecular scaled dense films may obtain a film have high gas barrier, high transparency, a high coverage rate and high uniformity but these methods not only require expensive instrument but also needs to repeatedly deposit multiple barrier layers in order to achieve high barrier effect. Thus, it has time consuming and high cost problems. Furthermore, generally these methods use, for example, inorganic films such as SiO2 or organic/inorganic alternately deposited multi-layered films as a gas barrier film but has fracture and crack problems due to bad flexibility when applied in flexible electronic devices to further result in shortening device lifetime.
Solution blending is currently one of extensively used methods to prepare a composite film because it is simple, fast and easy to mass production. Solution blending can be used to prepare a super high gas barrier film. Solution blending by adding graphene or its derivatives in a polymer to effectively increase gas barrier property of a resulting composite is reported. Although the gas barrier property of a composite can be improved after blending with graphene, the degree of improvement on the gas barrier property is very limited and the gas barrier property of the composite is still far away from the requirement for flexible electronic products having a difference by a few orders of magnitude.
Sadasivuni et al. reported in 2013 a poly(isobutylene-co-isoprene)/graphene composite film having an oxygen transmission rate of 28.4 cc/m2/day (K. Sadasivuni, A. Saiter, N. Gautier, S. Thomas, Y. Grohens, Effect of molecular interactions on the performance of poly(isobutylene-co-isoprene)/graphene and clay nanocomposites, Colloid Polym Sci, 291 (2013) 1729˜1740); and Jin, et al. reported a Nylon 11/graphene composite film having an oxygen transmission rate of 14.9 cc/m2/day (J. Jin, R. Rafiq, Y. Q. Gill, M. Song, Preparation and characterization of high performance of graphene/nylon nanocomposites, European Polymer Journal, 49 (2013) 2617˜2626). The difference between the reported composite films and the requirement (OTR<10−1˜10−6 cc/m2/day) for flexible electronic products is about 2˜8 orders of magnitude.
Generally, to achieve an organic/inorganic composite film having high gas barrier should consider the following factors: (1) inorganic substance should be uniformly dispersed in polymer matrix; (2) inorganic substance should have strong interaction with polymers; (3) inorganic substance has a large aspect ratio; and (4) inorganic substance can be piled up or aligned more densely as the concentration of the inorganic substance in polymer matrix is increased, disregard of aggregation of inorganic particles, so as to increase the degree of gas blockage.
Furthermore, a method combining solution blending and isothermal recrystallization to prepare a composite file being high gas barrier and high transparent is easier than to other film forming methods and can enhance the gas barrier performance but the long post processing for the composite film is required. Thus, the long post processing should be shortened for industrial continuous production processes and how to achieve the crystalline-like barrier effect is an important task for the industries.
On the other hand, the cross-linking reaction usually is used to suppress mobility or flexibility of polymer chains to reduce free volume so as to enhance the gas barrier performance. When a composite film is prepared by solution blending, the post cross-linking reaction usually is performed in the prior art, if the film forming property during coating processing from a polymer solution is considered. The post cross-linking reaction can be performed by a long period time of thermal processing or dipping in a chemical cross-linking agent but the long post cross-linking reaction cannot be simplified and also requires a large-scaled thermal processing device. It requires the high production cost and large and also has an uneven heating problem, particular for a large film.